Other authors in antiquity, however, were more likely to write about white crows than black swans.[2] This is probably a consequence of the paucity of swans and an abundance of crows. Juvenal, himself, wrote in his Satire VII that a "Happy man is rare - rarer than a white crow" ("Felix ille tamen corvo quoque rarior albo").[2] The ancient Greeks had the expression "seeing a white crow" ("λευκον ιδειν κορακα"). Not surprisingly, Aristophanes (c.446 BC - c.386 BC) mentions white crows in his play, The Birds.

The 99% blackness of soot is quite black; but, as I wrote in a previous article (Very White and Very Black, November 23, 2011), a more advanced form of soot, carbon nanotubes, can do much better. Arrays of vertically-aligned carbon nanotubes are quite black over a wide range of wavelength, and they can absorb more than 99.955% of incident light at visible wavelengths.[3-4] The supposed mechanism is that the forest of nanotubes has a multitude of holes and gaps to trap light; that is, incident light must make many multiple reflections to exit.

"Because of this time-reversal analogy to a laser, such absorbers are called anti-lasers... So far, anti-lasers have only been realized in one-dimensional structures onto which laser light was directed from opposite sides. Our approach is much more general: we were able to show that even arbitrarily complicated structures in two or three dimensions can perfectly absorb a suitably tailored wave. In this way, this novel concept can also be used for a much wider range of applications."[6-7]

"Waves that are being scattered in a complex way are really all around us - think about a mobile phonesignal that is reflected several times before it reaches your cell phone... This multiple scattering is made practical use of in so-called random lasers. Such exotic lasers are based on a disordered medium with a random internal structure that can trap light and emit a very complicated, system-specific laser field when supplied with energy."[7]

As shown in the above photo, the device consists of a microwavewaveguide and a central absorbing antenna filled with a random arrangement of Tefloncylinders. The cylinders act like stones in a puddle of water reflecting water waves; but, in this case, they scatter microwaves to create a complex wave pattern in which the reflected microwaves overlap and interfere with each other.[7] This enables efficient absorption by the central antenna, and this absorption was experimentally measured to be 99.8%.[7]

As Kebin Fan, a research assistant professor at Duke explains, "Typical CPAs have only one variable, the material's thickness... We have three: the cylinders' radius, height and periodicity. This gives us a lot more room to tailor these modes and put them in the frequency spectrum where we want them, giving us a lot of flexibility for tailoring the CPAs."[9]